In recent years, as electronic elements employed in a communication device such as a mobile phone are miniaturized with high performance at a high frequency range, demands for electronic elements such as an LC composite electronic element or a common mode filter capable of exhibiting a high attenuation capability at a high frequency range abruptly increase.
Currently, coils of LC composite electronic elements or the common mode filters are made of a magnetic substance such as Ni—Cu—Zn-based ferrite or a nonmagnetic Cu—Zn-based ferrite or dielectric material. However, such a substance has a relatively high dielectric constant of approximately 8 to 15 and is susceptible to a stray capacitance. For this reason, such a substance has a limitation in application to a high frequency environment, and it is demanded to provide a material having a lower relative dielectric constant (for example, 4.9 or lower).
In particular, it is difficult to implement a dielectric constant lower than 5, suitable for a recent high-frequency environment using a crystal substance such as mullite or forsterite having a dielectric constant of 6 to 7. Thus, it is demanded to develop a material using glass having a low-dielectric constant.
LC composite electronic elements or common mode filters are formed by co-firing different materials (for example, a capacitor material and a coil material). For this reason, it is necessary to match the linear expansion coefficients between different materials as close as possible.
In addition, it is desirable to use a conductive material containing silver (Ag) in order to reduce a cost of the conductive material or a direct current (DC) resistance. Furthermore, it is desirable to use a material sinterable at a low temperature equal to or lower than a melting point of Ag (for example, equal to or lower than 950° C.).
As such a ceramic material capable of a low-temperature sintering, for example, JP H09-241068A proposed a ceramic substrate in which a thermal expansion coefficient is controlled based on a ratio between quartz and fused quartz (amorphous silica) with a low relative dielectric constant of approximately 4.2.
However, the low-temperature sintering ceramic material disclosed in JP H09-241068A has a linear expansion coefficient of approximately 80×10−7/° C., which is still different from a linear expansion coefficient of ferrite, 95×10−7/° C. to 115×10−7/° C. Therefore, it was difficult to perform excellent unification co-firing of different materials for preventing a crack caused by a difference of the linear expansion coefficient.
In the unification co-firing of ferrite, typically, a glass component of B2O3 is dispersed into ferrite, and a glass component of a sintered body is reduced. For this reason, sinterability is degraded, and silver (Ag) used in the internal electrode is easily dispersed into the sintered body. Therefore, reduction/deformation of the internal electrode is promoted, and properties as an electronic element and reliability may be degraded.